In recent years, problems concerning electrostatic have been paid attention to. Such problems include the charging of the surface of a molding of plastic, glass, or the like, which causes contamination of the surface by, for example, dust, or failure or breaking-down of ICs and LSIs due to voltage with high electrostatic, or malfunction of electronic equipment due to electromagnetic noises. In view of this, it has become important to impart antistatic properties to resin.
Known methods for imparting antistatic properties to resin include coating of an antistatic agent such as a surface active agent on the resin surface, and mixing of an antistatic agent into resin. The method for coating an antistatic agent on the resin surface, however, has the problem of lacking in practical usability as an antistatic resin with persistency because antistatic properties decrease significantly after a long period. On the other hand, the problem with the method for mixing an antistatic agent into resin is that because of poor compatibility between antistatic agents and resin, the antistatic agent bleeds out on the surface of the molding, thus decreasing an antistatic effect. In addition, such problems exist that because of the humidity dependent properties of antistatic agents such as surface active agents, their antistatic effect may be deactivated under low humidity, or it may require at least 1 to 3 days to exhibit their antistatic effect after forming the resin, thus causing a delayed action.
In addition, a method for mixing carbon black or carbon fiber into resin is proposed. This method, however, has such problems that a transparent molding cannot be obtained and that the choice of color for a molding is limited.
Japanese Unexamined Patent Publication Nos. 64-9258 and 2-255852, aiming to overcome the problems of poor compatibility between antistatic agents and resin and of their poor dispersivility in vinyl chloride resin, disclose antistatic agents that utilize perchlorate such as ammonium perchlorate and lithium perchlorate. In addition, an antistatic composition that contains polyamide resin, polyether esteramide resin, aliphatic polyester, polylactic resin, thermoplastic elastomer and unvulcanized rubber, and alkali metal salt or alkaline earth metal salt is proposed (International Publication No. WO 01/79354A1). The above perchlorate, however, has the problem of impairing the thermo stability of vinyl chloride. In addition, sufficient antistatic properties may not be obtained depending on the kind of metal salt used for the antistatic composition. Furthermore, there are such drawbacks in utilizing perchlorate that when wrapping metal with the obtained film or sheet, the metal surface may corrode, rust, or be contaminated. In addition, when alkali metal salt is dissolved in polymerizable monomer, this polymerizable monomer is heated at the time of dissolution. This starts the polymerization of the monomer and thus may not realize a uniform surface coat layer. On the other hand, when alkali metal salt such as lithium perchlorate is dissolved in alcohol or an ethers solvent, the alkali metal salt gives off heat so intensely when dissolved that it may be impossible to control the heating. This presents the problem of not being applicable industrially.
As a method for imparting electric resistivity to polyolefin resin, a method for adding hydrophilic resin is proposed (by, e.g., Japanese Unexamined Patent Publication Nos. 4-198308 and 7-126446). This method, however, requires the hydrophilic resin to be added at more than 10 percent by weight of the polyolefin resin in order for the resin to exhibit practically sufficient antistatic properties. This presents the problem of impairing the physical properties of the substrate resin; for example, the strength of a molding decreases. In addition, when humidity is low, moisture on the resin surface decreases and so does antistatic properties resulting from moisture, presenting the problem of significantly impairing antistatic properties.
In addition, Japanese Unexamined Patent Publication No. 9-227743 discloses a transparent antistatic composition in which vinyl chloride resin, plasticizer, and lithium bis(trifluoromethanesulfonyl)imide are blended. However, the blended amount of the lithium bis(trifluoromethanesulfonyl)imide is large with respect to the vinyl chloride resin, and this deteriorates thermo stability; when heated at 120° C. for 30 minutes, the composition becomes blackish brown, thus presenting the problem of losing transparency and antistatic properties.